Quails employ anaerobic burst flight to escape predators and the Quetzalcoatlus northropi have most likely used it during launch and climb out, then transition to soaring.
Now, I have read these papers, from Marden, Witton and C.J. Pennycuick
I won't play pretend I really don't know that much about bird flight mechanics, so I easily got confused reading them.
How does anaerobic flight performance scale with mass?